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| Circuit Diagram (Proteus Simulation of the Project) |
The basic working principle of the fan
is that, when the temperature increases the fan starts rotating. We have kept a
DC motor in place of fan in the above proteus simulation of the project.
The circuit exploits the property of
Thermistor to operate the DC Fan. Thermistor is a kind of temperature dependent
resistor and its resistance varies depending on the temperature in its
vicinity. There are two types of Thermistors- NTC and PTC.
Negative temperature coefficient (NTC)
Thermistor decreases its resistance when the temperature increases while
Positive temperature coefficient (PTC) increases its resistance when the
temperature increases. Thermistors are bead like resistors available from 100
ohms to 10K or more values. Here a 4.7K NTC Thermistor is used. IC 741 is used
as a voltage comparator to switch on the DC fan. Its INV input (pin2) gets an
adjustable voltage through VR while its Non-INV (pin3) input gets voltage
through a potential divider comprising R1 and the Thermistor. Thus the voltage
at pin3 depends on the conductivity of the thermistor.
When the temperature is
normal (as set by VR), pin3 gets higher voltage than pin2 and makes the output
of IC high. This high output keeps T1 off since its base is positive. DC fan
remains off in this condition. When the temperature increases above the value
set by VR, resistance of Thermistor decreases and the voltage at pin3
decreases. As a result, output of IC becomes low to switch on T1.
A small brush less DC fan
(one used in computers) turns on to increase the air circulation. When the
temperature returns normal, Fan automatically turns off. Diode 1N4007 is
necessary to remove back EMF when T1 turns off.
(If you need further help about
this comment below.)
I keep getting this error when switching to ARES "PINSWAP property must be placed in pinout script 0402"
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